Variable Frequency Transformer for Robust Control of Power Flow between Synchronous Power Networks

Variable frequency transformer (VFT) is a power flow control machine connected between two electrical networks without necessarily synchronized voltages. Although VFT is generally an active power control device, there has been a VFT configuration introduced to control both active and reactive power flowing between networks. This paper presents a controller to control active and reactive power flow which is robust against parametric uncertainty. Therefore, the proposed controller not only controls both the outputs through the whole operating range but also does not lose its functions because of the variation of some of the parameters over time. Besides, the ability of the controller to perform in a noisy condition is verified. In this paper, the controller design process is discussed, and simulation results are illustrated to show the merits of the proposed controller.

I. Introduction

As electrical networks grow due to economic and practical reasons, controlling power flow through desired paths becomes unavoidable. In general, power flow rules may lead to congestion in transmission systems, therefore, it would be preferable to determine the amount of active and reactive power flowing through some of the lines directly. Thus, several practical methods have been introduced to gain control on flowing power in electrical networks, including phase-shifting transformers, back-to-back high voltage direct current (HVDC) systems, and variable frequency transformers (VFT).